This invention relates to electronic speed governors used in internal combustion engines. More particularly, this invention relates to governors for small engines used in lawnmowers, snowblowers, generators, and the like.
Typical prior art electronic governors use an actuator and a return spring to maintain throttle plate position. The actuator has a coil that is responsive to a control signal from the electronic circuit or microprocessor. In response to the control signal, the actuator drives the throttle in a first direction. The return spring is connected to oppose the actuator force and tends to pull the throttle in the opposite direction.
A major disadvantage of these prior art electronic governors is that they have a very slow response time. The slow response time is due to several factors, including the spring force of the return spring. The spring force varies with throttle position. Near the wide open throttle position, the spring force is about 6 ounces of force, corresponding to 50 to 70 percent of the actuator force. Near the closed throttle position, the spring force is less, about 2 ounces of force.
The effect of the return spring force is apparent from the basic force equation of the system: EQU F=M.times.A, (1)
Where
F=the total force of the actuator, spring, linkage, and throttle plate system; PA1 M=the total mass of the moving components in the system; and PA1 A=the acceleration of the system. PA1 F.sub.A =the actuator force; PA1 F.sub.T =the force on the throttle plate caused by moving air; PA1 F.sub.F =the friction force of the system components; and PA1 F.sub.S =the spring force of the return spring.
It is also clear that EQU A=F/M. (2)
It is apparent from equation (2) that either increasing the system force F and/or decreasing its mass M will increase the acceleration A of the system. Since the acceleration A of the system is inversely proportional to the system response time, an increase in acceleration A will decrease the response time.
The total system force F is given by the following equation: EQU F=F.sub.A -F.sub.T -F.sub.F -F.sub.S, (3)
Where
The total force of the system may be increased by simply increasing the actuator force F.sub.A, which generally means that a larger actuator must be used. However, the use of large actuators is very expensive and increases the weight of the governor.
The throttle plate force F.sub.T can theoretically be decreased to increase the total system force F. However, decreasing the throttle plate force may result in an unsafe, overspeed condition since the throttle plate force is typically necessary to close the throttle if there is a break in the linkage between the actuator and the throttle plate.
Since the friction force F.sub.F is always minimized but never totally eliminated, it is difficult to reduce this negative force.
Since prior art systems typically require a return spring to oppose the actuator force, prior art systems cannot eliminate the spring force F.sub.S.
Therefore, the only way prior art systems could increase the total force F and thus increase the acceleration A and decrease the response time was to increase the actuator force F.sub.A. As stated above, this solution required a heavier and more expensive actuator.